The Ba/Si(100)-2 × 1 interface: II. XPS, BIS and synchrotron PS studies of Schottky-barrier formation

In the preceding paper Surf. Sci. 260 (1992) 97] we have reported the results of XPS and XAES studies of silicide formation at the Ba/Si(100) interface at elevated temperatures. In this paper we present the results of XPS, BIS, and synchroton PS studies on the same system but at room temperature. We find that Ba grows layer by layer on the Si substrate and that electron energy losses and final state effects are important for the correct interpretation of the data. Observed shifts in the Si 2p core levels are ascribed to a lowering of the Schottky barrier and are explained with the model presented by Mönch Phys. Rev. Lett. 58 (1987) 1260], while measured shifts in the Ba 4d core levels are related to the reduction of the silicon work function. This model requires the presence of metal induced gap states (MIGS) which are indeed observed with BIS. Here we find increasing spectral intensity near the Fermi level upon Ba deposition. This intensity is assigned to Ba 5d states which probably fulfill the role of the MIGS in Mönch's model.